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An Observational Study of Tropical Cyclone Spin-Up in Supertyphoon Jangmi and Hurricane Georges

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An Observational Study of Tropical Cyclone Spin-Up in Supertyphoon Jangmi and Hurricane Georges Calhoun: The NPS Institutional Archive DSpace Repository Theses and Dissertations 1. Thesis and Dissertation Collection, all items 2011-12 An observational study of tropical cyclone spin-up in Supertyphoon Jangmi and Hurricane Georges Sanger, Neil T. Monterey, California. Naval Postgraduate School http://hdl.handle.net/10945/10686 Downloaded from NPS Archive: Calhoun NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA DISSERTATION AN OBSERVATIONAL STUDY OF TROPICAL CYCLONE SPIN-UP IN SUPERTYPHOON JANGMI AND HURRICANE GEORGES by Neil T. Sanger December 2011 Dissertation Supervisor: Michael T. Montgomery Approved for public release; distribution is unlimited THIS PAGE INTENTIONALLY LEFT BLANK REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188) Washington DC 20503. 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED December 2011 Dissertation 4. TITLE AND SUBTITLE: An Observational Study of Tropical Cyclone Spin-Up 5. FUNDING NUMBERS in Supertyphoon Jangmi and Hurricane Georges 6. AUTHOR(S) Neil T. Sanger 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING Naval Postgraduate School ORGANIZATION REPORT Monterey, CA 93943-5000 NUMBER 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING / MONITORING N/A AGENCY REPORT NUMBER 11. SUPPLEMENTARY NOTES The views expressed in this thesis are those of the author and do not reflect the official policy or position of the Department of Defense or the U.S. Government. IRB Protocol Number: N/A. 12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Approved for public release; distribution is unlimited A 13. ABSTRACT (maximum 200 words) An observational study of tropical cyclone spin-up is performed using dropsondes and satellite imagery from Supertyphoon Jangmi and Hurricane Georges. Additionally, ELDORA data are analyzed in Tropical Storm Jangmi. The dropsonde analysis shows that the peak tangential wind occurs persistently within the boundary layer and suggests that significant supergradient winds are present there. However, as a result of data limitations arising from asymmetries and irregular placement of dropsondes in both time and space, a strongly conclusive statement about the presence of supergradient winds in Tropical Storm Jangmi is not possible. A dense deployment of dropsondes across the RMW is recommended to resolve the pressure gradient with sufficient accuracy to validate that supergradient winds exist at the tropical storm stage. An examination of ELDORA data in Tropical Storm Jangmi indicates that multiple rotating updrafts are present near the eye underneath cold cloud tops of ≤ -65°C. Analysis of the infrared satellite imagery from both storms suggests that rotating updrafts are omnipresent before and during rapid intensification. The findings of this study support a new theoretical model positing that spin-up of the maximum winds occurs within the boundary layer and rotating deep convective cells are predominant during tropical cyclone intensification. 14. SUBJECT TERMS Tropical cyclone spin-up, vortical hot towers, Supertyphoon Jangmi, 15. NUMBER OF Hurricane Georges, tropical cyclone intensification, rapid intensification, rotating deep convection, PAGES tropical cyclone boundary layer. 187 16. PRICE CODE 17. SECURITY 18. SECURITY 19. SECURITY 20. LIMITATION CLASSIFICATION OF CLASSIFICATION OF THIS CLASSIFICATION OF OF ABSTRACT REPORT PAGE ABSTRACT Unclassified Unclassified Unclassified UU NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Prescribed by ANSI Std. 239-18 i THIS PAGE INTENTIONALLY LEFT BLANK ii Approved for public release; distribution is unlimited AN OBSERVATIONAL STUDY OF TROPICAL CYCLONE SPIN-UP IN SUPERTYPHOON JANGMI AND HURRICANE GEORGES Neil T. Sanger Lieutenant Colonel, United States Air Force B.S., Florida State University, 1994 M.H.R., University of Oklahoma, 1997 M.S., Texas A&M University, 1999 Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY IN METEOROLOGY from the NAVAL POSTGRADUATE SCHOOL December 2011 Author: __________________________________________________ Neil T. Sanger Approved by: ______________________ _______________________ Michael Montgomery Russell Elsberry Professor of Meteorology Professor of Meteorology Dissertation Supervisor ______________________ _______________________ Patrick Harr Peter Black Professor of Meteorology Professor of Meteorology ______________________ _______________________ Francis Giraldo Roger Smith Professor of Mathematics Professor of Meteorology Approved by: _________________________________________________________ Wendell Nuss, Chair, Department of Meteorology Approved by: _________________________________________________________ Douglas Moses, Vice Provost for Academic Affairs iii THIS PAGE INTENTIONALLY LEFT BLANK iv ABSTRACT An observational study of tropical cyclone spin-up is performed using dropsondes and satellite imagery from Supertyphoon Jangmi and Hurricane Georges. Additionally, ELDORA data are analyzed in Tropical Storm Jangmi. The dropsonde analysis shows that the peak tangential wind occurs persistently within the boundary layer and suggests that significant supergradient winds are present there. However, as a result of data limitations arising from asymmetries and irregular placement of dropsondes in both time and space, a strongly conclusive statement about the presence of supergradient winds in Tropical Storm Jangmi is not possible. A dense deployment of dropsondes across the RMW is recommended to resolve the pressure gradient with sufficient accuracy to validate that supergradient winds exist at the tropical storm stage. An examination of ELDORA data in Tropical Storm Jangmi indicates that multiple rotating updrafts are present near the eye underneath cold cloud tops of ≤ -65°C. Analysis of the infrared satellite imagery from both storms suggests that rotating updrafts are omnipresent before and during rapid intensification. The findings of this study support a new theoretical model positing that spin-up of the maximum winds occurs within the boundary layer and rotating deep convective cells are predominant during tropical cyclone intensification. v THIS PAGE INTENTIONALLY LEFT BLANK vi TABLE OF CONTENTS I. INTRODUCTION........................................................................................................1 A. HISTORICAL OVERVIEW ..........................................................................1 B. CHALLENGES OF TROPICAL CYCLONE INTENSIFICATION FORECASTING ..............................................................................................3 C. SCIENTIFIC EXPLORATION OF SPIN-UP ..............................................6 1. Motivation .............................................................................................6 2. Inner Core and Outer Core Definitions .............................................7 3. Hypotheses to be Tested in This Thesis..............................................7 4. Relation of Current Research to Recent Hurricane Field Experiments ..........................................................................................8 a. TCS08/T-PARC .........................................................................8 b. IFEX ........................................................................................10 5. Data Collection Missions in Hurricane Georges and Supertyphoon Jangmi ........................................................................10 6. Outline of This Study .........................................................................10 II. TROPICAL CYCLONE SPIN-UP REEXAMINED ..............................................13 A. IMPORTANCE OF THE BOUNDARY LAYER .......................................13 B. DEFINITIONS OF THE BOUNDARY LAYER ........................................14 1. Thermodynamic Definition ...............................................................14 2. Dynamical Definition .........................................................................15 3. Challenges in Defining the Boundary Layer in the Inner Core.....15 4. Recent Observations ..........................................................................17 5. Boundary Layer Definitions Used in this Thesis .............................18 C. TROPICAL CYCLONE SPIN-UP THEORIES REVIEWED..................19 1. Conventional Spin-Up Theory ..........................................................19 2. WISHE Spin-Up Theory ...................................................................20 3. Rotating Deep Convection .................................................................22 a. Asymmetric Viewpoint in Detail .............................................23 b. Axisymmetric Viewpoint in Detail ..........................................26 III. DATA AND METHODOLOGY ..............................................................................29
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